Long-period thermal storage accumulators

ABSTRACT

A long-period storage accumulator for storing heat water is used as a storing medium. The water is enclosed in large thin-walled containers which are arranged under the ground. The water pressure forces acting on the container walls are carried by the surrounding of the container.

REFERENCE TO OTHER APPLICATIONS

This application is a division of our co-pending application Ser. No.860,191, filed Dec. 15, 1977, now U.S. Pat. No. 4,174,009, which in turnwas a continuation of application Ser. No. 616,256, filed Sept. 24,1975, now abandoned.

THE PRIOR ART

Thermal storage accumulators based on the heating of water are known.They have not been used industrially as long-period accumulators becausethe investment into the storage containers, determined by the requiredcontainer volumes and internal pressures, makes economic operationimpossible. The weight of steel for a thermal storage accumulator with aone week capacity in a nuclear power station is larger than the weightof the water to be stored in it. Long-period storage accumulators aredefined as accumulators which permit as nearly as possible full-loadoperation of the steam generator during entire weekends and/or wasteheat utilisation with a time shift of weeks or even months.

THE OBJECT OF THE INVENTION

One object of the invention is an improvement in the utilisation ofprimary energy, particularly in nuclear power stations, by means ofthermal storage accumulators which are charged with excess primary heatand/or waste heat and held in readiness over prolonged periods. Afurther object of the invention is a storage system and storageaccumulators with containers, the stresses in which are not carried bythe container material but by soil or water. In this way, sufficientlylarge containers can be made economically.

DESCRIPTION OF THE INVENTION

According to the invention, caverns in the ground or, for containersplaced under water, external water pressure is used to take up thepressure of the storage medium. This invention can be used for variousstorage media and storage temperatures.

Three embodiment options according to the invention will be described:

1. Heat sink storage accumulator for condensers of power stations and/ordistrict refrigeration systems.

2. Hot water storage accumulator under pressure enclosed in a cavern forthe supply of power stations and/or district heating systems with heatenergy.

3. Storage accumulators under pressure placed beneath the water level ofa natural or artificial water basin for the supply of power stationsand/or district heating systems with heat energy.

The claimed storage accumulators can also be used to advantage incombination and, furthermore, individual distinguishing features of theinvention can be used outside the field of long-period storageaccumulators. In the exposition below, specific materials and values ofquantities are given for the sole purpose of facilitating understandingand should be regarded as examples only.

1. DESCRIPTION OF A HEAT SINK STORAGE ACCUMULATOR

The efficiency and power output of a power station can be enhanced inmaking use of the invention by widening the operating temperature dropduring peak-load periods with the help of heat sink storageaccumulators. A cavern is created by salt-solution mining in a salt rockformation, the volume of which should amount to 1000 m³ per MW ofelectrical output power of the power station. A saturated water-NaCLsolution is contained in the storage accumulator, which serves as thestorage medium. During part-load periods, the machine set of the powerstation drives a refrigeration compressor which compresses arefrigerant, preferably an aliphatic hydrocarbon.

The refrigerant is then condensed in a condenser by a through-flow ofe.g. river water and thereupon fed in the liquid state via a throttlevalve into the cavern accumulator. Evaporation of the refrigerantproceeds in the accumulator with simultaneous crystallisation of thestorage medium. A peak load, the steam discharged from the power stationturbine is fed into a condenser, in which a hydrocarbon, e.g. propane,evaporates. This vapour is fed to a low-temperature turbine, the poweroutput of which contributes to supply the peak load demand. Thecondensation of the propane vapour takes place in a condenser, which isarranged in the storage accumulator. During the periods of peak load,the power station operates as a two-component turbine circuit system.The temperature drop is increased by the amount between +35° C. and -21°C. The efficiency of the power station increases from 33% to 42%. Thepower output of the plant rises thereby from 1,000 MW to 1,280 NW. Anetwork for the supply of refrigeration plants can also be fed from thesame storage accumulator, using the excess power of the power stationduring low-load periods.

2. DESCRIPTION OF A HOT WATER STORAGE ACCUMULATOR IN A CAVERN

Nuclear power reactors usually generate steam. The feed water extractedfrom the condenser is heated to near boiling temperature by tapped steamextracted from the turbine. The steam enthalpy amounts to 2,890 kJ/kg,whilst the usable enthalpy of the feed water is about 1,235 kJ/kg. Thepower generation capacity of a turbine plant can become substantiallylarger if the tapped steam, which withdraws almost half the enthalpy, isnot extracted from the turbine but flows through all the turbine stagesand produces work.

According to the invention, during low-load periods, the excess thermalenergy is used, via the tapped steam or by direct extraction from thecirculation, for heating a storage water reserve placed in anunderground cavern. The storage water thereby reaches near boilingtemperature. In peak-load operation, the heat of the water, if necessaryby the interposition of a heat exchanger, is drawn on for pre-heatingthe reactor feed water, so that, during this condition of operation, notapped steam is extracted from the turbines, whereby the turbines becomecapable of producing about 30% more power output. The depth of thestorage accumulator cavern is so chosen that the boiling pressure cancarry the rock cylinder lying above the accumulator, so that thesubstantial pressure forces are fully absorbed by the rock. 3.DESCRIPTION OF THE UNDERWATER STORAGE ACCUMULATOR

If lakes are available or if the power station is situated near the sea,the invention provides the arrangement of a storage accumulator at adepth below the water surface such that, at the foot of the accumulator,the pressure forces of the enclosed storage water are preferablybalanced by the external water pressure. In this way, it is possible touse plastic foils as storage accumulator walls. Since the hot water oflower specific weight lies underneath the sea water of higher specificweight, the top cover forms an unstable membrane. For this reason, amembrane of a specific weight exceeding 1 g/cm³ is chosen.

Insofar as gas is used for insulation, according to the invention, thisgas is compressed to the same pressure as the outside and the insidemedia. However, the invention also provides for the thermal insulationto be accomplished by the water itself. Thus water containers accordingto the inventiom may remain open downwards, i.e. without additionalinsulation. Towards the walls and the ceiling, a structure is insertednear the inner wall surface which prevents convection of the waterlayers adjacent to the wall so that the water penetrating this structureacts as an insulator. For the optimum matching of the temperatureprevailing inside the accumulator and diminishing in the downwarddirection to the temperatures of the water flows to be fed in orextracted, the invention provides tubes or hoses with apertures whichcan be adjusted in height.

The invention will be described below together with individual elementsaccording to the invention.

FIG. 1 shows an energy sink storage accumulator according to theinvention together with a power station.

FIGS. 2a, 2b and 2c shows a hot water storage accumulator together witha power station.

FIG. 3 shows an internally situated insulation.

FIG. 4b shows a storage accumulator with externally situated insulation.

FIG. 4a shows an insulating element used in the storage accumulator ofFIG. 4b.

FIG. 5 shows a storage accumulator with a flooded cavern.

FIG. 6 shows pumps and turbines to overcome pressure discontinuities.

FIG. 7a shows tubes with apertures adjustable in height.

FIGS. 7b-7e show various float designs used in FIG. 7a.

FIG. 8 shows an accumulator for storage in layers with equipment forincreasing the temperature difference between the layers.

FIG. 9 shows a storage accumulator for undersea installation.

FIG. 10 shows a storage accumulator for undersea installation,especially for low temperatures.

FIG. 11 shows a lake as a storage accumulator.

FIG. 12 shows a power station plant with a waste heat storageaccumulator.

FIG. 1 shows the circuit diagram of a storage accumulator and powerstation components. The reactor 1 generates permanently a thermal poweroutput of 2,380 MW. The steam turbine 2 generates permanently amechanical power output of a little over 1,000 MW, which, in normaloperation, is converted by the generator 3 into 1,000 MW of electricalpower output. In normal operation and in low-load operation, thecondensation takes place in the condenser 4 at a mean temperature ofabout 35° C. In low-load operation, the refrigeration compressor 5 isengaged by the clutch 6. This compressor withdraws a mechanical poweroutput of up to 230 MW from the common shaft and draws in gaseousrefrigerant from the upper region of the storage accumulator via thepipeline 25'. The heat of condensation of the refrigerant is transferredvia the pipeline 25" in the condenser 7 to the cooling water, which isstill cold. The evaporation of the refrigerant takes place after itsdischarge through the orifice plate 28. Eutectic crystals 9 are producedby the evaporation. Since these are somewhat lighter than the saturatedaequeous salt solution, they first wander upwards and subsequently alongthe arrow 35 until the entire storage accumulator is filled withcrystals. A condenser 11 is situated in the upper region of the storageaccumulator 10. At peak load, the condensation of the discharged steamtakes place in the evaporator 12 which is filled with propane 13. Thepropane vapour so formed drives the secondary turbine 14 which suppliesup to 130 MW to generator 3 via the coupling 15. In this way, up to1,130 MW are available for electrical power generation during thepeak-load period. The duration of the peak-load operation depends on thepower of the refrigeration compressor 5 and on the size of the latentheat storage accumulator 10. For an accumulator of one week's capacity,a latent energy of 4.6·10¹¹ kJ is required. Such an accumulator needs avolume of 1.82·10⁶ m³.

An annular hollow body 21 floats on the level 20 of the storagesubstance. The hollow body forms the steam side collector manifold forthe plastic condenser tubes 11. These tubes open out into a weighed-downannular tube 22. The collector 21 communicates with the discharge sideof the turbine 14 via the pipeline 23. The pipeline 23 may also beconnected to a distributor plate similar to the orifice plate 28 insteadof a closed condenser 21, 11, 22, so that the condensation of thedischarged steam takes place in the upper regions of the accumulatorcontents, and the condensate collects above the level 20 so as to be fedback into the circuit via the pipeline 24" and the pump 24'. Thecompressed refrigerant flows through the pipeline 25" into the condenser26 and from there, via a condensate pump 27, into the orifice plate 28.When the compressor is in operation, refrigerant condensate 29 entersthere into the brine which is pumped up via the central tube 30 from theaccumulator bottom 31.

A eutectic brine/ice dispersion forms in the foil cylinder 32 which isbraced against the annular collector tube 22 by ropes 33. Thisdispersion is displaced by the brine flowing outward along the arrow 35.An orifice plate 36 is arranged in the lower region of the tube 30 inorder to convey the brine. A small partial flow of the refigerantcondensate, which is pumped by the pump 37, emerges through the orificeplate. In this way, an emulsion 38 is formed in the tube 30. Owing toits low density, the emulsion rises. The maximum energy sink capacity isreached when the entire volume of the accumulator is filled with thebrine/ice dispersion, wherein the proportion of the brine is allowed todiminish down to 20%.

The construction of the storage accumulator takes place preferably insalt rock by solution mining with water. No lining of the cavern isrequired because a saturated aequeous salt solution is formed whereby afurther dissolution of the salt rock is prevented.

The storage accumulator thus forms an energy sink, which leads to anincrease of the temperature drop between the steam generator 1 and thestorage accumulator, which serves as a condenser during peak-loadoperation. A peak-load is thereby provided by the turbine 14. Duringlow-load operation, on the other hand, the compressor 5 is driven.

Refrigeration brine may be additionally extracted through the pipeline34 for a supply network to refrigeration plants. The brine throughputflows through the pipeline 39 back into the storage accumulator.

FIG. 2a shows a hot water storage accumulator. The steam generator 40supplies the high-pressure turbine 41 and the intermediate superheater42 with fresh steam. The superheated steam proceeds via the pipeline 43into the low-pressure turbine 44. From there, tapped steam flows throughthe pipeline 45 into the feed water pre-heater 46. High-temperaturetapped steam enters via the pipeline 47 into the high-temperaturepre-heater 48 so that the feed water reaches the evaporator 40 at nearboiling temperature. The discharged steam flow reaches the condenser 50via the pipeline 49, whilst the condensate flows through the boiler feedpump 51 into the pre-heater 46.

By opening the valve in the pipeline 52, hot water enters the heatexchanger 53 of the cavern storage accumulator 54. The accumulator isplaced at such a depth that the rock column 55 has a weight equal to theprojected 56 multiplied by the internal pressure in the accumulator 54.

The accumulator wall consists of a plastic foil 57. The accumulatorspace is sub-divided by an intermediate plate 58 into two regions 54'and 54". This intermediate plate is weighed down by weights 59 and, ifnecessary, braced into a flat shape by ropes 60 which are carried bytension fittings 61. The region 54" is lined with an insulating layer52. The pipeline 63 with the pump 64 is situated between the two regions54' and 54".

The heat exchanger is traversed either by a flow of cold water (duringcharging) from the pump 65 or by a flow of hot water (duringdischarging) from the pump 66. In order to discharge the accumulator,the hot water traverses the heat exchanger 53 and thereby heats the feedwater flowing through the heat exchanger, as shown in FIG. 2b. The heatexchanger separates the turbine circulation from the storage accumulatorcirculation so that the hydrostatic pressure, if it exceeds the boilingpressure in the pipelines 52 and 67, does not act on the accumulatorwalls.

When charging the cooled water returns into the turbine circulation viathe pipeline 67 by the interposition of the pump 68, whilst the pump 65pumps cold accumulator water through the heat exchanger 53. The coldaccumulator water, after being heated up, discharges through theinoperative pump 66 (FIG. 2c). During the charging process, the water inthe space 54" expands. A corresponding quantity of cold water is pumpedby the pump 64 into the space 54'. A pipeline 69 communicates with thespace 54' and also, via the heat exchanger 70, with an insulated liquidgas accumulator 71.

The circuit diagram for discharging the accumulator is also shown inFIG. 2b. The cold boiler feed water is pumped by the pump 68 via thepipeline 67 into the heat exchanger 53 and fed via the pipeline 52 in ahot condition to the evaporator 40.

For this purpose, the pump 66 extracts hot water from the highest levelof the accumulator space 54". After transferring the heat to the feedwater, the hot water flows through the pump 65 back into the accumulatorspace.

An aliphatic hydrocarbon is preferably used as a gas cushion. Thetemperature in the liquid gas accumulator 71 is so chosen that it liesbelow the critical temperature of the gas. The valve 72 prevents thecondensation of the entire gas quantity.

The size of the reserve in the accumulator 71 is so chosen that theentire space 54' can be filled with gas at the boiling pressure of thestorage water. A pipeline 75 leads from the lower region of the storageaccumulator to the core of the reactor 40. In case of emergency, theportion within the accumulator which is below 100° may be used, via thevalve 76, for emergency cooling even without pump operation.

FIG. 3 shows the wall lining of the storage accumulator according toFIG. 2. A smooth rendering 81 is applied to the rock 80. A plastic foil82 closely fits this rendering. At specified distances, metal profiles83 formed as horizontal hoops are arranged and fastened to the rock 80by steel nails 84. The web 83a of the metal profile 83 is folded backand covers the heads of the nails 84. Undercut regions 85 are formedbetween the profile 83 and the wall 81, in which a fold of the plasticfoil 82 and metal hooks 86 are inserted. Recesses 87 are cut in thesehooks for suspending the tension cables 88. Clips 90 are stamped out inthe lower web 89 of the hook components, in which coolant tubes 91 areinserted. The foil 82 is thus made into a fold 82a in the region of thehooks and is fastened to the rock wall 80, 81 without being perforatedby nails. The insulation consists of layers 99 which are covered on theinside with a wire netting 93. These wire nets 93 are held in positionby rods 97 and ropes 98. The insulating material 99 consists ofhydraulically and thermally resistant mineral fibres or else of metalfibres, coal powder or coke and is permeable to water, whilst itprevents thermal convection and the mixing of water layers near the wallso that a temperature drop of up to 300° C. is sustained between thewire netting 93 and the cooling water tubes 91. Foils 96, e.g. ofaluminium, are arranged between the layers of the insulation 99. Thesefoils prevent vertical convection. The cooling water pipes 91 aretraversed by cold water which is at the same pressure as the waterenclosed within the accumulator so that, inside the insulating layer, atemperature gradient prevails between the accumulator water temperatureand the cooling water temperature and the foil 82 can never assumeexcessively high temperatures.

FIG. 4a shows another design of the storage accumulator. The accumulatorcontainer proper 100 consists of steel rings made of U-profiles, theflanges of which are welded together as shown at 101, whilst thevertical webs leave gaps 102 between each two profiles, whereby thelongitudinal expansion can be absorbed. The insulation is provided byhollow insulating elements 103.

FIG. 4b shows the design of such a hollow insulating element 103. Thewall 104, facing the accumulator container, has corrugations whichabsorb the longitudinal expansion. The conical wall 105 can yieldaccording to the broken line illustrated at 106 when the accumulatorcontainer 100 increases in its diameter. Mineral wool slabs 107 areplaced inside the annulus, between which intermediate layers 108 aresituated to prevent convection.

FIG. 5 shows a storage accumulator according to the invention which isarranged to float in a cavern. The accumulator container 110, the wallof which is insulated either by internal insulation, as shown in FIG. 3,or by external insulation, as shown in FIGS. 4a and 4b, floats in theflooded cavern 111. The accumulator wall is anchored to a supportingring 112. An annular bellows-type component 113 is joined to thesupporting ring. The bellows component carries the cover 114. This coveris overlaid with an insulating layer 115. Compressed gas or liquid underpressure is injected through a pipeline 117 into the space 116 above thecover. The cold water and hot water pipelines 118, 119 are connected topumps or turbines, respectively. The cold water pipeline alsocommunicates with an expansion tank 131 (FIG. 6).

According to the invention, the inside of the cavern 111 can also befilled with compressed air or nitrogen. In all cases, the storageaccumulator can also be placed inside a mountain, where the shaft may behorizontal, too.

FIG. 6 shows diagrammatically an arrangement according to the invention.The accumulator container 120 communicates, via a turbine 121 and a pump122, with an expansion container 123 covered by a membrane 133 and withthe heat exchanger 124. The valve batteries 125 and 126 are socontrolled during discharge that the hot water pipelines 127' and 127"are connected via the turbine 121, whilst the cold water pipelines 128'and 128" are connected via the pump 122.

Since the density of the cold water is greater than that of the hotwater, the turbine supplies, even without taking account ofefficiencies, less power than is needed by the pump 122. The powerdeficiency is balanced by a motor-generator 129. In the reverse flowcondition during discharging, the power generated by the turbine 121 maybe larger than the power absorbed by the pump 122. If so, themotor-generator 129 may be operated in a generating mode. The pipelines127 and 128 are then appropriately changed over. In conjunction withsuitable automatic control elements, the turbine and pump achieve acompensation of the hydrostatic column pressure in the pipes 127' and128' which span the height difference 130. In this way, the accumulatorcontainer 120 is relieved of hydrostatic pressure.

The tank 131 communicates with the inside of the cavern 132, whereby apressure forms inside the cavern which results from the heightdifference 130.

FIG. 7a shows the design of the feeding and extraction pipelines. Sincetemperature stratification forms in the accumulator and the need arisesto perform feeding and extraction at optimum temperatures, the inventionprovides the use of tubes 140 which can be adjusted in height. Toprevent turbulence, a float 141 can be arranged at the end of the tube140 which can be adjusted to the desired height by means of a winch 142or by changing the gas quantity in a hollow body 143 situated inside thefloat 141.

FIG. 7b shows the cross-section of the float with a float body 143 andthe suction apertures 144 situated on top for the induction of hotwater.

FIG. 7c shows the design of the float for the induction of cold water.

FIG. 7d shows the float for the discharge of warm water and and FIG. 7eshows the float for the discharge of cold water.

FIG. 8 shows a circuit diagram which serves for the optimisation of thetemperature gradient inside the storage accumulator. The pipe 152extracts water from the cold region 151 and cools this water in the heatexchanger 153 so that even colder water emerges at the bottom 154,whilst the pipe 155 extracts warm water from the upper region, heats itup in the heat exchanger 156 of the heat pump 157 and returns this waterthrough the pipe 158, situated at a greater height, into the hotterregion 150.

FIG. 9, which is not to scale, shows an accumulator according to theinvention, which is arranged at the bottom of the sea 160. The outerwall 161 is formed as a body of revolution and increases upwards in itswall thickness because it has to resist the internal pressure whichincreases in the upward direction. According to the invention, this wallconsists preferably of strips made of glass fibre reinforced syntheticmaterial and has on its interior wall an isolating layer 162.

The space 165 serves as an expansion chamber for the changing density ofthe water enclosed in the storage accumulator space 166. Alternatively,the accumulator can be operated at constant mass. However, the enclosedstorage water can also be extracted. This procedure depends on theexpansion bellows portion 167 of the foil 163 having approximately thedimensions of the wall 161.

The cover of the accumulator container consists of an outside wall 168which is preferably made of plastic foil. Tension ropes 169 are attachedto this wall which carry a steel wire net 170. The steel wire net ispanelled with a fine-mesh wire gauze 171.

A layer 172 of sand or stones is placed above this net structure and,above this layer 172, a further layer 173 of mineral wool. The weight,less the buoyance of the layer 172, must be larger per unit of area thanthe pressure difference resulting from the density difference betweenthe hot water inside the container and the sea water outside thecontainer, multiplied by the height difference 174. If a pressuredifference remains, it is overcome by the pump 164.

In charging or discharging, hot water is conducted through the pipeline175'. The turbine-driven pump 176 overcomes the excess pressure in thepipeline 175' due to the depth postion in the sea. The pipeline 177 isrelieved by the turbine-driven pump 178. The depth below sea level mustbe chosen in accordance with the boiling pressure. At 350° C. watertemperature, for example, the required depth amounts to about 1,650 m.

FIG. 10 shows a modified arrangement in a lake. If the bottom of thelake is accessible, anchors 180 are fixed in the bottom. The coveringfoil 182 is held in a horizontal position by ropes 181. A wire netting183 is preferably suspended underneath the covering foil. Mineral woolor, at lower temperatures, an organic fibre wool is placed inside thespace 184 so formed.

Tubes 185 with apertures which can be adjusted in height are situatedinside the storage accumulator.

If the lake bottom is marshy, an arrangement shown on the right is used.The covering foil 186 is weighed down by weights 188 which are evenlydistributed. A float 187 is associated with each weight. The volume ofthe floats is larger than that corresponding to the residual weight ofthe bodies 188.

FIG. 11 shows another arrangement of a storage accumulator which can beembodied in lakes of which the total volume is approximately equal tothe desired accumulator volume. As before, tension anchors 180 orweights 190 are arranged at the bottom 199 of the lake. A covering 182,183, 184 is placed at a depth 191, which leads to a preliminarypressurisation inside the storage accumulator 192 to a value higher thanthe boiling pressure of the stored water. The upper region 193 remainsfull of cold lake water. Surrounding foil lip 194 which separate the twowater layers from each other are provided to seal against the risingshores of the lake.

FIG. 12 shows an example of the application of a low-temperature storageaccumulator 200, according to the invention which is placed in a lake201, communicating with a river 202. The tapped steam pipelines 203',203" and 203'" are connected to the condensers 204', 204" and 204'". Inaddition, feed water pre-heaters 205', 205" and 205'" are provided,which, in an appropriate control position of the valves 206', 206"206'", can absorb the tapped steam. The main condenser 207 is connected,via a pipeline 208, to the lower region 209' of the storage accumulator200. By swivelling the tubes 210', the desired water temperature can befed in.

During peak-load operation, the cold water, via the main condenser 207,the valve 211, the pump 212 and the pipeline 213, reaches theintermediate region 209" of the storage accumulator 200. At a sufficientlow power station load, the condensation takes place in one of thecondensers 204. If the condenser temperature is high enough, the coolingwater extracted from the region 209" and fed, via the valve 214', intothe pipeline 208, whilst the valve 214" is shut and, after heating upthrough the pump 212 and the pipeline 215, is conveyed into the upperregion 209'" of the storage accumulator.

In peak-load operation, hot water may, in addition, be withdrawn fromthe upper region 209'" and supplied, via the pipeline 215, the valve 216and the pump 217, to the heat exchanger 218 for heating the feed water.In order to withdraw the heat, the pump 219 pumps hot water into thedistrict heating network 220. This hot water is returned either into thelower region 209' or the intermediate region 209" by appropriate controlof the valves 221' and 221". If the heat extraction by the districtheating network 220 is insufficient, feed water is bled from time totime via the pipeline 222 into the river 202. Out of consideration forthe least possible thermal pollution of the river, the bleeding takesplace at times when the river water is particularly cool or when theriver flow is particularly large. A corresponding amount of fresh wateris returned from the lake into the storage accumulator via the pipeline223.

We claim:
 1. A combination of a long period heat storage accumulatoradapted to contain a large volume of water and a power station, saidaccumulator having means for filling and removing water therefrom andsaid power station having a turbine, a refrigeration compressor having aliquified refrigerant and a clutch for operatively connecting saidturbine and said compressor; the improvement comprising in that saidaccumulator is contained within a cavern formed in a salt rock formationwhereby the pressure of the water in the accumulator is contained by therock formation, in that the water comprises a saturated salt solutionobtained by dissolution of the salt rock formation, in that theaccumulator has a heat exchanger therein acting as a condenser for theturbine, in that means are provided for feeding a liquified refrigerantinto the accumulator whereby a brine mixture is formed, and in that ameans is provided for bringing a brine ice mixture into contact with theheat exchanger.
 2. A combination according to claim 1 wherein the powerstation has a supplementary turbine adapted to be operated by a gaseousform of a low boiling point liquid and an evaporator for evaporating thelow boiling point liquid, the improvement further comprising in having ameans connecting said supplementary turbine to said heat exchangerwhereby said low boiling point liquid is condensed by said heatexchanger.
 3. A combination according to claim 2 wherein said gaseousform is insoluable in water.
 4. A combination according to claim 2whereby the refrigeration compressor is operatively connected by saidclutch to said turbine only during low load periods of said powerstation and the supplementary turbine is run by said low boiling pointliquid only during peak load periods of said power station.
 5. A longperiod heat storage accumulator adapted to contain a large volume ofwater where the accumulator is for use with a power station and wherethe accumulator has means for filling and removing water therefrom; theimprovement comprising in that said accumulator is contained within acavern formed in a salt rock formation whereby the pressure of the waterin the accumulator is contained by the rock formation, and in that thewater comprises a saturated salt solution obtained by dissolution of thesalt rock formation.
 6. A long period heat storage accumulator adaptedto contain a large volume of water where the accumulator is for use witha power station and where the accumulator has means for filling andremoving water thereform; the improvement comprising in that saidaccumulator is contained within a cavern formed from a rock formationwhereby the pressure of the water in the accumulator is contained by therock formation, in that the accumulator has a hollow cylinder arrangedin its upper region, in that the accumulator has perforated channelssituated beneath the hollow cylinder through which a refrigerantcondensate may enter, and in that the underside of the cylindercommunicates with the bottom region of the accumulator by means of atube.
 7. A long period heat storage accumulator according to claim 6wherein a portion of the refrigerant condensate is adapted to be fedinto said tube through said perforated channels.